After a dozen-year stretch in Uncanny Valley, Robert Zemeckis has returned to the world of live-action with the substance abuse drama Flight. It’s not the smoothest ride. The film’s alcoholism plotline veers toward the generic, the symbolism is often so blunt as to be laughable, and the supporting players are mostly one-note.

What keeps it on course, however, is the compassionate but honest character study at its core. Zemeckis and screenwriter John Gatins (Real Steel) have an iron grip on who Captain William “Whip” Whitaker is and what makes him tick, and Denzel Washington‘s grounded performance maintains the audience’s sympathy without sugarcoating Whip’s nasty side.

When we first meet Whip, he’s starting out a work day like any other. He wakes up still drunk from the night before, a naked flight attendant asleep beside him, and snorts a line of coke to get his mind back into focus before rushing off to his airplane. Once there, he proceeds to fix himself an orange juice with three vodkas and inhales from the oxygen tank. The flight hits a bit of turbulence early on, thanks to a rough storm, but even in his booze-soaked state Whip is a capable enough pilot to guide his plane to clear skies.

He’s still in that less-than-optimal condition when the flight takes a much more serious turn. An equipment malfunction sends the plane into a dangerous nosedive, forcing Whip to pull some unorthodox stunts in an attempt to save everyone on board. His quick thinking has him hailed as a hero by the media, but his private struggles are just beginning. A federal agency launches an investigation into the incident, uncovering incriminiating evidence of Whip’s alcoholism. Should he be convicted for criminal negligence and manslaughter, he could spend the rest of his life in prison.

It’s edgy material for a filmmaker better known for his family fare, but Zemeckis doesn’t flinch. Addiction is a nasty, R-rated disease, and Flight treats it as such. There’s no polite averting of the eyes when characters snort or shoot drugs, or pass out half-naked. Even more harrowing is the plane crash, an intense and graphic action set piece that had me alternately gasping and holding my breath.

But then, subtlety isn’t Flight’s stock in trade. This is the kind of movie where the camera zooms in as a single tear drop’s from a man’s eye, where an AA member recalls how his lies would “walk [him] out that door” as our dishonest protagonist literally walks out a door, where Whip’s drug dealer pal (John Goodman) makes his entrance to the Rolling Stones’ “Sympathy for the Devil.” Religious references are frequent and heavyhanded. “An act of God” is cited as the cause of the plane crash, which took out the steeple of a Pentecostal church, while Whip’s rescue is “nothing short of a miracle.” But they don’t add up to much of anything.

Supporting characters are treated with similar bluntness. Don Cheadle and Bruce Greenwood do their best as Whip’s lawyer and a union representative, respectively, but their talents are wasted in these stock roles. Brit actress Kelly Reilly fares worst of all as Whip’s recovering addict love interest Nicole, who’s less an actual character than a symbolism-laden plot device. Although the film goes to pains to set up a generic junkie backstory for her, it’s never clear why she’s interested in Whip or what she wants out of the relationship, so it’s difficult to muster up any interest in their romance.

But Flight largely works in spite of such clumsiness, thanks to its compelling and complicated protagonist. Zemeckis and Washington aren’t afraid to let Whip be unlikeable, and they’re upfront about the fact that Whip is a terrible husband, father, employee, and friend. Even more interesting is the decision to show how alcohol brings out Whip’s charming side. In one scene, a giddy Whip suggests to Nicole that they fly to the Caribbean. She’s wary of his obvious drunkenness, and we are too, and yet it’s tough not to be a little bit seduced by his infectious energy and mischievous smile. It’s all too easy at that moment to understand what it is about the bottle that calls to Whip so loudly.

What brings Whip’s disparate sides together, and what keeps him from being purely despicable, is Washington’s dedicated performance. Even when Whip is at his cockiest, there’s self-loathing bubbling just beneath the surface; even when he’s at his most contemptible, there’s a sense that he wants desperately to be better than he is. The umpteenth shot of Whip trying and failing to resist temptation is just as heartbreaking as the first, because Washington makes the internal struggle feel like a fresh one each time.

The investigation and Whip’s issues come to a climax at a tense hearing, where Whip finds himself faced at a crossroads. It’s to Zemeckis’ and Gatins’ credit that the decision is a genuinely tough one, with sky-high stakes and no easy answer. Unfortunately, the film fizzles once he makes his choice. Having completed Whip’s arc, Zemeckis promptly diminishes it by tying up loose ends in the most ham-fisted ways possible, and what was for two hours a complex portrayal of destructive disease becomes in its last fifteen minutes an afterschool special. How ironic that a film about a miraculous landing should have so much trouble sticking its own.